The primate occipital lobe is divided into a number of separate visual areas which can be distinguished from one another on the basis of their topographic organization and their afferent and efferent connections. In the rhesus monkey, or macaque, several of the visual areas outside the striate cortex can also be distinguished by the functional properties of their constituent cells. For example, the analysis of binocular disparity is emphasized in one region (area V2), color in another area (V4), and movement within the visual field in yet another region (the "movement" area). The present proposal would employ the macaque in an analysis and comparison of the laminar and columnar organization of three adjoining visual areas, V3, V3A, and V4, using a combination of physiological and anatomical techniques. The goal is to determine what types of neuronal circuitry are involved in the building up of the specialized functional classes of cells found in each area. The receptive field properties of cells will be analyzed in single-unit recordings from awake, unanesthetized animals. Particular attention will be paid to any differences in cellular properties among the different cortical layers, and to any cell groupings that should indicate the presence of functional columns. Retrograde tracing techniques will be used to determine the laminar distribution of cells projecting to different regions. The results of each experiment will be charted on a two-dimensional reconstruction of the cortical surface that will provide a detailed, accurate map of even highly convoluted regions of the hemisphere. This program continues the general approach which has proven very successful in studying the primary visual cortex, and it may lead to new insights into the organization and function of high visual areas of the brain.